Slot antennas can be implemented with a gap in a metal surface. Simple resonant slot antenna geometries include a half wavelength (.lambda./2) slot antenna 110 as shown in prior art FIG. 1 and a quarter wavelength (.lambda./4) slot antenna 210 as shown in prior art FIG. 2. For a .lambda./2 slot antenna 110, the length 140 of the slot 120 is a half wavelength and both ends of the slot 120 are closed, while for a .lambda./4 slot antenna 210, the length 240 of the slot 220 is a quarter wavelength and only one end of the slot 220 is closed while the other end is open. A conductive ground plane 130, 230 surrounds each slot 120, 220. The .lambda./2 slot antenna 110 is driven differentially from an excitation port having a positive node 170 and a negative node 175 located near the closed end of the slot 120 and perpendicular to the slot 120 as shown. The .lambda./4 slot antenna 210 is also driven differentially from an excitation port having a positive node 270 and a negative node 275 located near the closed end of the slot 220 and perpendicular to the slot 220 as shown.
Some radiotelephones require signal reception in more than one frequency band. More than one slot antenna can be used in a radiotelephone to obtain reception in the required bands, however, separate antennas require separate excitation ports and individual electronic tuning mechanisms, which can get expensive. Thus, there is a need for an antenna with a single excitation port and multi-band reception capability.